My U.S. Pat. No. 5,482,441, issued Jan. 9, 1996, discloses a system which can be utilized to desalinate seawater. The system includes a rotary variable displacement liquid pump and rotary metering device driven by a drive motor to pump liquid through containment structure and a single reverse osmosis filter.
My U.S. Pat. No. 5,462,414, issued Oct. 31, 1995 and U.S. Pat. No. 5,628,198, issued May 13, 1997, disclose other approaches to solving certain problems inherent in the prior art and have features in common, including the use of a reversible piston which cooperates with filter means to produce desalinated water.
U.S. Pat. No. 4,793,153, issued Dec. 27, 1998, discloses a prior art hydraulic circuit employing a reversible piston to accomplish "energy recovery" in a mixed-phase motor in a refrigeration system.
U.S. Pat. No. 4,367,140, issued Jan. 4, 1983, discloses apparatus for the reverse osmosis purification of water or other fluid wherein the water is forced into a module containing a membrane under pressure using two piston-cylinder assemblies mechanically inter-connected.
U.S. Pat. No. 6,017,200, issued Jan. 25, 2000, discloses an energy-recovery pump or pumping system which includes, in a double-action embodiment, first and second cylinders wherein respective first and second pistons, mounted to a common reciprocal reciprocating piston shaft, are mounted for reciprocating motion.
It is known to pump sea water or other liquid seriatim through a series of reverse osmosis filters, however, such arrangements are inefficient in that downstream filters tend to clog and operate with less efficiency since they receive essentially undiluted concentrate from upstream filters. This results in high operating costs and inefficiencies in the system.